Detect area of a PNG that is not transparent with HTML

To detect an area of a PNG that is not transparent:

•  You need to first get the buffer
•  You need to get 32-bits reference of that buffer
•  Scan 0 widths to find x1 edge
•  Scan width 0 to find x2 edge
•  Height to find the y1 edge
•  Height 0 to find the y2 edge